The field of this invention relates to camera shutters and more particularly to camera shutters of the mechanical type. Particularly, the invention relates to the device for controlling the emittance of light onto photographic film in common cameras, especially in single lens reflex type cameras. As will be seen hereinafter, the employment of the new type of camera shutter described and claimed herein permits exposure times over a large dynamic range and permits exposure times that are significantly less than obtainable by conventional mechanical shutters.
Currently, the most common shutters employed in cameras are mechanical shutters; that is, those which rely upon mechanical elements which obstruct the passage of light from the camera lens system on its pathway to the film. There are three main types of mechanical shutters commonly used. Those are between the lens shutters, behind the lens shutters, and focal point shutters. Generally, such mechanical shutters work by imposing an opaque object, usually metal foil, between the light of the outside world and photographic film. When a photographic record is desired, the opaque object is removed long enough to expose the film and then return to the closed position. Movement of mechanical shutters are usually powered by springs or electrically operated solenoids that move one or more metal foil blades.
In between the lens or behind the lens shutters, the blade movement, acceleration, stoppage and reversal of masses consume time and energy and limit the obtainable total exposure time to a minimum of 1/1000th or 1/2000th of a second. Higher speeds require stronger driving springs, and parts able to withstand the wear and tear. This results in a larger and costlier shutter.
A focal plane shutter is usually a slit moving across the film. At high speeds, fast moving objects will change position with various strips of exposure. At such speeds all conventional mechanical shutters, are likely to exhibit various distortions and seeming optical illusions. At high speeds, fast moving mechanical parts also cause the vibration of the camera which often blurs the photographed image.
From time to time experimental work has been accomplished on use of other than mechanical optical modulators in order to control the transmission of light through an aperture as a function of time. Some devices which have been experimented with include electrooptic modulators which employ electrical fields to induce bifringence in the shutter material, i.e., polarization of light passing through the device dependent upon voltage; acoustooptic modulators which employ sound waves to scatter and defract light; magnetooptic modulators which use magnetic fields to change the polarization or transmission of light, and the like. However, such systems have generally been extremely expensive and met with little or no success in the real commercial world of practical everyday usable cameras.
It can therefore be seen that a faster shutter in conventional inexpensive cameras could conceivably open a whole new realm of photography to both amateur and professional photographers. The use of such a faster and inexpensive shutter would allow good quality pictures of high speed. Areas of use and demand for such a shutter might include action sports and many natural phenomena. Additionally, high speed industrial processes could be successfully analyzed photographically. Also such a device could be used in movie cameras with high speed repetition rates and in scientific photography where low vibrations are required.
Accordingly, one object of this invention is to provide a new camera shutter which avoids the deficiencies of conventional mechanical shutters.
A more specific object of this invention is to provide camera shutters that are considerably faster than conventional mechanical shutters and can obtain shutter speeds within the range of 10.sup.-4 s to 10.sup.-6 s, considerably faster than conventional shutters which are ordinarily limited to 10.sup.-3 s.
Yet another object of this invention is to provide a shutter which minimizes blur, distortion and optical paradoxes that often occur at high speeds with conventional mechanical shutters. Yet another object of this invention is to provide a shutter which requires less energy to operate than conventional mechanical shutters, thus freeing stored camera energy for accomplishing other tasks.
An even further object of the invention is to provide a much simpler shutter which employs no springs, cams, holding leafs or the like, thus significantly eliminating possibilities of mechanical failure.
A still further object of this invention is to provide a non-mechanical type shutter which can operate at high speeds with virtually no mechanical vibration.
Still another more specific object of the invention is to provide a camera shutter which employs frustrated total internal reflection principles to provide a shutter which has as its only movement the small expansion or contraction of piezoelectric ceramics which in turn move the prism components of the lenses from a light reflecting gap open position to a light transmitting gap closed position.
The method and manner of accomplishing these and other objects of the invention will become apparent from the detailed description which follows hereinafter.